1. Field of the Invention
This invention relates to an improvement of a powder supplying device.
2. Description of the Related Art
It is well known as shown in Japanese Patent Laid-Open No. Hei 3-25321 to provide a loss-in-weight type powder supplying device in which a powder hopper (a storing tank) is supported by a weighing device, a flow rate of powder supplied by a vibratory feeder fixed to the powder hopper is calculated with reference to a reducing amount of weight of the powder hopper per hour measured by a weight sensor of the weighing device and then a supplying flow rate of the powder is feed-back controlled to a target value.
In a prior art powder supplying device in which specified flow rate is required, a vibration of an electromagnetic feeder is feed-back controlled in response to weight data obtained by high speed sampling and then a high level or a low level of vibration of the electromagnetic feeder is controlled in such a way that it becomes a set flow rate acting as a target value.
In addition, as another prior art, it is well known in a manufacturing stage for an engine valve for an automobile to perform overlaying with a laser clad. The laser clad machining operation is a method for supplying metallic powder to a laser radiating part to make local melting and fixing of different kinds of metals, wherein a gear type rotary feeder has been used as a powder supplying device for performing a continuous supplying of a small amount of overlaying powder to a groove having a narrow circumference of a valve.
In the device for supplying a specified flow rate of powder using the electromagnetic feeder, an analog output signal of a weight sensor is converted by an A/D converter in a control device into a digital value and inputted. This sampling (inputting) frequency is about 100 to 200 Hz. In addition, since the electromagnetic feeder utilized a motion with a frequency of about 100 to 500 Hz under an electromagnetic vibration, there was a problem that a mechanical vibration of this feeder was transmitted to the weight sensor and it was overlapped onto an output signal of the weight sensor as a noise component. As a result this structure was not suitable for a specified flow rate for supplying of a small amount overlaying powder in a manufacturing step for an engine valve which was an application of the prior art.
Although it may be considered to use a low pass filter in order to remove noise, it generates a problem that it is necessary to apply a low pass filter having a cut-off frequency which is sufficiently lower than an electromagnetic vibration of the electromagnetic feeder, resulting in that a response characteristic of the weight sensor is deteriorates and a response characteristic of a flow rate control is lacking.
Then, in the case of the aforesaid prior art (a rotary feeder), there was a problem that its response characteristic was poor and an instantaneous response characteristic was lacking in addition to the problems that a pulsation of flow rate caused by a pitch of a gear was produced or its size was large and the device could not be mounted near a supplying point.